Differential control device



NQv. 19, 1935.- w. G. HILLEN Er A1.

DIFFERENTIAL CONTROL DEVICE 5 Sheets-Sheet l Filed Dec, 14, 1932 Nov.`19, 1935. w. G. HILLEN ET AL 2,;021727 D1:FFERENTIALV CONTROL DEVICE Filed Dec. 14, 1932 5 Sheets-Sheet 2 Pfad-erw WBazley William 62H11 len I ATTORNEY Nov. 19, 1935. w. G. H| EN ET AL 42,021,727

DIFFERENTIAL CONTROL DEVICE A TTORNEY Nov. 19, 1935. w, G, HILLN ET L 2,021,721

DIFFERENTIAL CONTROL DEVICE A TTORNEY Nov. l19, 1935.

w. G. HILLEN ET An. 2,021,727

DIFFERENTIAL CONTROL DEVICE Filed Dec. 14, 1952 5 Sheets-Sheet 5 BY /A-` y ATTORNEY `nated.

parent from t ings, `i

Petrie# NW1 il??? a DIFEERENTIAL Aoon'rltor; pizvon Shiba-u, Toilry'orJapai-i,

j Frederic .W."Bailey,' ,East Orange, N. J., as-

signers, by mesne assignments, to Carrier Engi-A meering Corporation, Newark, N. J., a corporaf tion of New York f Application December 14, 1932, Serial No. 647,186

11 Claims.

This invention relates to the control of the temperature of one fluid in accordance with uncontrolled changes in the rtemperature of .a'

second fluid, and further, the invention relates to a new and improved apparatus for providing such control.

'I'he principal object of the invention is to p rovide a control system in which the temperature of one fluid may vary in response to variations in the temperature of another fluid.

Another object of the invention is to provide a control system in which a differential be-l tween two mediums is established, the differential varying in accordance with variations in the temperature of one of the mediums.

Still a further object is to provide a control system which will maintain one medium ata constant temperature until a s econd medium reaches a predetermined temperature at which time the temperature of the first medium will vary in accordance with variations in the temperature of the second medium. v w

Another object of the invention is to provide a single control instrume t in which two thermoresponsive elements opp se each other in such a manner that the pressure of a' fluid controlled by the instrument is aiected by 'both elements.

A feature of the invention resides in the provision of a control ,instrument in which frictional packing and stuiiing boxes have been elimi-I Another feature resides in balancing the pressures withinv the instrument in such a way that a. high degree of sensitivityl is secured.

A further feature resides in the provision of a control instrument having two thermostatic elementsA and providing a means at one en d of one of the yelements for varying -independently the.;

action of either element. n

Still another feature resides in the provision of a control instrument vhaving two thermostatic elements composed of .the same material, one of Lthe elementslbeingf'longer than the other, so

a .that Qneelqmem; may/expand a greater amount,

element.:

per unit of itemperaturevariation, than the other .Otherlo Jects, rdffeatures relating to novelty vin -"designfand :construction will be more ap- .ffoilowing description Aand draw- .Fl eatery sectioned View of one ention'; 1

` atie illustration of the :fvariatio s in1-temperati1re of o'ne medium, under the control of an instrument such as illustrated in Fig. 1, with respect to a second medium,

Fig. 3 is a fragmentary plan view, partly in section, of another control instrument embodying the principles of the invention,

Fig: y4 is a diagrammatic illustration of how the temperature of one mediummay be caused to vary with respect to the temperature of another medium by an instrument such as shown in Fig. 3,

Fig. 5 shows a sectional plan view of another 4control instrument embodying the principlesof the invention, l I

Fig. 6 shows the manner in whichthe temperature of one medium may be causedto vary 15 with respect tofanother medium `when an instrument such as illustrated in Fig. 5 fis inuenced by the temperatures of both mediums,

Fig. 7 is a sectional plan view adapted to carry out the invention when applied to a control sys- 2 0 tem in which it is desired to vary the temperature of one medium with respect to another, as

shownin the temperature diagram of Fig. 8,

Fig.' 9 illustrates an air conditioning systeml having a temperature control system embodying 25 the instrument shown in Fig. 1 and adapted to vary the temperature within an enclosure according tothe diagram of Fig. 2,

Fig. 10 shows a diagrammatic view of an air conditioning system in which some ofthe temperature affecting instrumentalities are operated by an vinstrument such as shown in Fig. 3 according to the temperature diagram of Fig. 4,

Fig. 1l represents an air conditioning system in which an instrument, such as shown in Fig. 5, comprises an element of the temperature control system adapted to vary the temperature of "air discharged from the systemfin accordance with tfxithe temperature diagram of Fig. 6, and

..Fig 12 illustrates, in diagrammatic form, an 40 lair conditioning system ,in which an instrument Before` going into. an extendeddiscussionnofithe 45ml constructional `details of the fthennostats;of;Figs,.

The various ther)mostats,sh(WYE/(litigs.v 5

spense; tliemeerture changes, than@@stiltsereairfvelves-v Stlllnlvisait@vv hjead: matige-..

effect, .the` each :of .theinrsi-'closure memben's is operatively attached to a thermostaticvelement pressure of a iluid passing through the valve is affected by changes in temperature in both mediums. P

'Ihis variation lin pressure may be utilized, for example, in an air conditioning system, to operate various temperature affecting elements, such as heaters, water valves, dampers, and the like, to control the temperature of one of the mediums affecting the instrument when either or both the head and/or the seat move to vary the pressure.

With particular reference to Fig. 1, similar designations referring to similar parts, I3 represents a metal tube having a relativelyl large coefficient of expansion, securely attached at one of its ends to the interior of a hollow casting I4. Threaded, or otherwise suitably attached, on the other end of the tube I3 is a tubular extension member I5. Within the tube, and coaxial therewith, is a metal rod I6, preferably invar, but necessarily a material having a coeiilcient of expansion smaller than the coeiiicient of expansion of the tube I3. One end of the rod I 6 has formed thereon ahead I1 adapted tocooperate with a seat I8, as will be hereinafter described, and the other end is threaded into a crown I9. 'Ihe crown l I9 ts loosely within the tubular extension I5 and is adapted to be engagedby shoulders 20, formed on the inner surface of extension I5. A screw 2l, threaded through the top of. crown I9 engages the end of rod I6 and provides a means of adjusting the rod and locking it in position.

A cap 22 is threaded-into the end of extension casting I4 in such a manner that the instrument .may be fastened to a suitable panel; as by clamping the panel between flange 24 and the casting I 4.l

Into the 'other end of the casting I4, a second* casting 25 is threaded, thereby forming a chamber 26. 'Ihe casting I,2li has a smooth cylindrical A plugr 28, having a ground seat I8 formed in one, end is threaded into the plunger 21 and is-adapted to securely clamp a diaphragm 29 therebetween. 'Y An axial passageway 30 is drilled through the.

bore adapted to vreceive the plunger 21.

plunger 21 and the plug 28 communicating with a radial .passageway`3l in the plunger 21. lThe passage 3l in turn communicates with a discharge passage 32, formed in the casting 25, the outer end of which is enlarged and may be threaded to receive the end of a suitable pipe or tube (not shown). Similarly, a passageway 36, en-

` larged and threaded at its outer end,is adapted to admit a iiuid under pressure, from any suitable source, to the chamber 26.

At the opposite end of the p1unger 21, a piug 35 is threaded therein and engagesand securely formed thereon. The head is partially rounded, as illustrated, and terminates in a fiat anvil.

The diaphragm 29 has its periphery tightly fastened, as by a clamping ring 33, to the innerl face of the casting 25. In a like manner, the 5 diaphragm 36 is secured to the Vouter face of casting 25 by the clamping ring 31. 'The casting is recessed atA both ends, as indicated by the reference numeral 34, so that the plunger may move backward and forward as will be hereinafter de- 10 scribed. l

'I'he casting 25 has threaded on its outer end, although obviously, it might be formed integrally therewith, a ange 39. Near the periphery of the iiange 39 a series of holes are formed adapted 15 to receive the reduced end portions of support rods 40. Nuts 4I are threaded on the rods 40 to securely fasten'the rods to the iiange 39. In a similar manner, another flange 42 is secured to the opposite ends of the rods 46.

At the center of the flange 42, a hollow plug 43 is threaded therein, the outer end of the plug having an enlarged keyway 44 in which a key may be inserted to enable the plug 43 to be rotated. The inner end of plug 43 is enlarged and 25 rounded, as illustrated, the purpose of which will be hereinafter described. 'Ihe plug 43 is internally threaded to engagel corresponding threads on a rod 45 and the rod is provided at one end with a keyway 46 whereby .therod may be rotated. 30

Applicant prefers to make the rod 45 and the support rods 4II of invar.v Although other metal may be used, it is of particular importance that these rods 45 and 40 be oi the same material or materials having the same coeiiicient of expan- 3,; sion. A tube 41, preferably, but not necessarily, made of the same metal as the tube I3, is loosely suppo-rted by; but not attached to, the rounded portions ofthe plugs 35 and 43. Silk reducing cones 48 are attached to each end of the tube 41 to keep out dust, dirt, and other extraneous) matter. I y

The tubes I3and 41 may be made of the same material or rthey may be made of materials having vdifferent coefilcients of expansion, and'fur- 45 ther, they 4may be of equal or 'different lengths.

In the illustration (Fig. 1), applicant has chosen, for purposes. which will later be made apparent, to describe tube I3 as being three times as long as tube 41 and as being madelof the same mate- 50 rial. vIn that the tubes have the same coefficient of expansion (inches per inch per,` degree) but are of different lengths, the rate of expansion (inches per degree). of tube I3 will be three times the rate of expansion of tube 41. Hence, for one de- 5,

54 respectively, tlrrough the air washer and de- 65 liver the combination to an enclosure through a duct 5I. A volume of return air may bypass the air washer through duct 55 to, augment and attemperate the air from the washer, the mixture being controlled by dampers 56 and 51 respective- 70'.

ly. A reheater 56 is adapted to supply any heat required under the control of a device such Vas yalve 59. Thermostat 6I), of well known design is adapted to vary the pressure of compressed air in the line II and hence, vary the air pressureA '15 I.

perature of the air delivered to the enclosure may be regulated, both in summer and winter.

To illustrate this regulation in connection with the invention, a differential thermostat of the type-shown in Fig. 1, generally designated 64, is mounted yin` the returnv air duct 52 with the thermal tubeI3subjected to the temperature in the duct andthe ytube 41 'iniiuenced by the temperature of outside air.` The line 65 represents a pipe leading. from a source of compressed air to the entrancefpassage 38 of the thermostat, and the line 66, having a leak device 61 therein, connects the discharge passage 32 of the thermostat 64 to the air motor 68, adapted to operate bypass damper 56 the air motor 69 adapted to operate air washer damper 51, and the diaphragm valve 59. Valve 59 isof lthe type which is held open by a springand is closed by an increase in air pressure onits operating diaphragm. As ccntemplated in this particular instance, valve 59 will be completely open when there is no air pressure on line 66; will start to close when the pressure reaches 2 pounds per square inch and will be fully closed when the pressure `reaches 5 pounds per square inch. Likewise, the dampers 56 are adapted tobe open when there is no air pressure on the motor 68. The motor 68 will start to close the dampers when the pressure in line 66 rises above 5 pounds per square inch and the dampers will be closed a maximum amount when the air pressure reaches 10 pounds per square inch. Motor 69 operates the air washer dampers 51 conversely, that is, the dampers are open a minimum amount when the air pressure is below 5 pounds per square inch and the dampers will be fully opened when the pressure reaches 10 pounds per square inch.

Considering the specic operation of the thermostat 64, this instrument is designed to control the pressure of compressed air so that the varia.- tion in air pressure will cause the steam valves 59 and dampers 56 and 51 to operate to control the temperature of air delivered to the enclosure according to a temperature curve such as the curve of Fig. 2. 'Ihat is, it is designed to hold a constant temperature within the enclosure until the temperature outside the enclosure rises above a predetermined point. Then the instrument will function to increase the temperatureI in the enclosure as the outside temperature increases.

As can be seen (Fig. 1) air pressure in the chamber 26, remembering that this air is compressed above atmospheric pressure, tends to force diaphragm 29, lconsequently plunger 21 and its associated parts, to the right until the head 35 engages the end of tube 41 or rests against the end of rod 45. By rotating the rod change in temperature of the return air affecting .thermal tubeV I3. Obviously, if the temperature in 52 rises, Itube I3 will expand, shoulders 20 will engage crown I9 and pull the invar rod I6 and its ead I1 away from the seat I8. This opening lwards its seat, thereby closing the valve.

of the air valve will increase the pressure in line 66 andthis increase in pressure will operate to close valve 59 and dampers 56 and to open dampers-51, thereby lowering the temperature of the air supplied to the enclosure. Conversely, should the temperature in duct 52 decrease, tube I3 will contract, rod I6 and head I1 will be carried to- To preventvhead I1 from jamming against seat IB and possibly ruining the instrument, a spring 23 is placed between the crown I9 and cap 22. Any

contraction of tube I3 after head I1 seats against I8 will cause a compression of the spring, thereby preventing any damage.

As was pointed out, as the outside temperature rises above a predetermined point, it is desired to raise the inside temperature. After adjusting the seat I8 by rod 45, as was previously explained, the plug 43 is rotated (holding rod 45 against rotation) until the tube 41 is resting rmly between the head of plug 35 and the head of plug 43 when the outside temperature is at the desired point, for example '70 F. If the outside temperature rises above 70 F., the tube 41 will expand and force the yplunger 21 to the left, hence, reducing the air pressure in line 66 and causing an increase in temperature in duct 5I. At this point, it should be remembered that any increase in outside temperature will be reflected by an increase in temperature Within the enclosure. -As waspreviously pointed out, tube I3 expands three times as much per degree rise in temperature as does tube 41. Hence, although tube 41 expands to close the valve', tube I3 expands to open it, thereby giving a diierential effect.

If, onthe other hand, the outside temperature is decreasing. the tube 41 will contract, allowing plunger 21 toxmove to the right. At the same time, the tube I3 will contract, moving the-head I1 to the right. When the outside temperature drops to 70 F., the head 35 Will engage the end of rod 45 and any further movement of the seat tothe right will be prevented. As the outside temperature falls below 70 the tube 41 will continue to contract, just resting lightly between' head 35 and plug 43.

With the foregoing in mind, it is evident that by turning plug 43 (without holding rod 45) the entire curve of Fig. 2 may be shifted vertically. The setting of rod 45 determines the point at which the inside temperature will be carried during the winter months, while the adjustment of plug 43 determines the point at which both elements of the thermostat function. By varying the length of the tubes I3 and 41,'the slope of the differential temperature line may be varied,

but for anyA given instrument, this slope is conve'ntion. Likewise, the hollow casting I4, casting 25, flange 24, plunger 21, diaphragms 29 and 36, clamping rings 33 and 21, and others, have their counterparts in Figs. 3, 5 and '7. Further, the plunger and the diaphragms are mounted in the same manner as was described in connection with Fig. l, with theexception that in each cf ,the gures, the plug 35 has been replaced by a plug having a similar function but which is slightly' diierent in shape. Since the same reference numerals are used for the same elements in all the drawings, this`spe'cication will not be further lengthened by consideration of these parts Figs. 3, 5 and '1. y

With particular reference to Fig. 3, a ilange 10 having atubular extension 1|, formed integrally therewith, is adapted to be threaded to one end of the casting 25. The flange 1I) has holes therein adapted to receive the reduced end portions of support rods 40, the rods being fastened as by nuts 4I. A flange 12,'having a portion of its inner face recessed as at13f, is securely attached to and supported by the rods 40. A metal tube 13, preferably of the same material as the tube I3, is attachedto and supported by, in any desired manner, the inside of the extension 1| of ilange 1|). Fixedly attached to the other end of the tube 13 is a hollow cap 14, the

4outer end of which is slightly concave.

An invar rod or the like, 18, having one end threaded, as indicated at 11, passes through aw hole 15 in the center of ange 12. The rod 18 also passes through, and is co-axial with, the tube 13 and terminates in a rounded head 18.

The head 18 is adapted to seat in a recessed portion of a plug 19, which plug is threaded into the plunger 21 in the same manner as plug 35 of Fig. 1. 4It is of particular importance to note that the threads 11 of rod 18 do not engage either the flange 12 or the hollow cap 14.

Threaded on the rod 18, and adapted toilt loosely in the recessed portion 13, is a nut 19 having a convex face Iwhich seats in the concave portion of the hollow cap 14. A key allows the nut to move longitudinally, but prevents .any rotation. A spring 8| is held in compression between an annular projection 82 of the rod 18 and the shoulders formed on the inside of the hollow cap 14. Threaded on the outer end of rod 18 are two nuts 83 which may be locked in position at any point between the ange. 12 and the end of the rod. A projection 84, on the /end of the rod, is adapted to receive a key for the purpose of rotating the rod.

The application of a differential thermostat 85, ofthe type shown in Fig. 3, to an air conditioning system is shown in Fig. 10. The apparatus shown in Figs. 9 and 10 is identical, except that differential thermostat has been substituted for 84. In this case, it is desired to lower the temperature of air supplied to an enclosure,

as the temperature outside the enclosure rises above a predetermined minimum. Hence, the element I3 of the thermostat 85 is placed in the duct 5| where it will respond to changes in temperature of the air supplied by fan 58. The element 13 (Fig. 3) is subjected to the inuence of outside' air supplied to the instrument through a sampling tube 88. As was previously explained, the valve 59 is open when there is no air pressure on the line 58; begins to close as the pressure rises above 2 pounds per square inch and is completely closed when the pressure reaches 5 pounds per squareinch. The dampers 58 and 51 are likewise operated in the same manner as was hereinbefore explained.

With reference to Figs. 3 and 10, it is apparent that as the temperature in duct 5| rises, the tube I3 responds by expanding. In so doing, the shoulders 28 engage the crown I9 and draw the head I1 away from its seat I8, thereby allowing the passage of air. Conversely, as was explained in connection with Fig. 1, contraction of the tube I3 returns the head I1 towards its seat.

By moving the plunger 21, hence seat I8 associated therewith, to the right or left, the thermostat may be set so that variations in air pres- 2,021,727 yin connection with the'following description of sure due to movement of tube I3 and head I1, will operate the valve 59 and dampers 58 and 51 to maintain constant, at any desired point, the temperature4 in duct 5I. In the instrument of Fig. 3, this is accomplished by rotating'rod 18. 5 As the temperature of the medium, in this case outside air, affecting tube 13 increases, the tube will expand, engage the nut 19-and carry the rod 18, on which the nut is threaded, to the right. The plunger 21, and its component parts, will 10 follow, as was previously noted, thereby opening the valve wider and increasing the pressure of air in discharge passage 32, which pressureaffects the dampers to cause a reduction in temperature in the duct 5|. 15

When the temperature aiecting 13 decreases, the tube will contract and, through spring 8|, transmit motion to the rod 18, thereby carrying the rod to the left. Obviously, this moves plunger 21 to the left, consequently reducing the open- 20 ing between head I1 and valve seat I8, hence, reducing the air pressure affecting the damper motors. As the outside temperature affecting 13 decreases, the inside temperature will rise. However, when the outside temperature falls be- 25 low a certain temperature, it is desired to-hold the inside temperature-constant. This is accomplished by turning the, nuts 83 until they just touch ilange 12 when the outside temperature has dropped to the desired level. It is apparent that 30 any further movement of the rod 18 to the left is effectively stopped. Further contraction of tube i13 will be taken up'by compression of spring 8|. Therefore, the thermostatic element I3 alone effects the openingand closing of the valve, hence 35 tending to hold a constant vtemperature in the duct 5I.

The instrument of Fig. 3- was designed primarily tovary the inside temperature, or. duct temperature, according to the diagram of Fig. 4. The 40 instrument is set, by adjusting rod 18, to hold a constant duct temperature of 70F. until the outside temperature rises to 73 F That is, the nuts 83 are in engagement with flange 12 as long as the outside temperature is '13 or below. As the 45 temperature rises above '13"A F. the tube'h13 expands so that with each 3 F. rise outside, the inside'temperature will be reduced 2 F. It is apparent that the plunger 21 may be set so that tube I3 will tend to hold any desired temperature and 50 that nuts 83 may be positioned to stop the action of tube 13 at any desired point, the temperatures stated being illustrative only.

- With reference to Fig. 5, the left hand portion r of the instrument is identical with the left hand 5" portions of Figs. 1 and 3, as was previously pointed out. IOn the right hand end of casting 25, a ange 18 (similar in all respects t'o flange 10 of Fig. 3), having a tubular extension 1 I, is threaded or otherwise suitably attached. The tubular extension 1| is adapted to receive and securely hold, in any desired fashion, one end of a metal tube 81, similar to the tube 13 of Fig. 3. The tube 81 is preferably, though'not necessarily, of the same metalas tube I3. Securely attached to the other end of tube 81 is a cap 88 having a plug 89 threaded in its head. The plug 8,5 is drilled axially and has a keyway cut therein. l

vAs was previously pointed out, flange 10 has 70 holes therein adaptedto receive and secure (as by nuts 4|) the reduced end portions of rods 40. Supported on the other ends of rods 4D is a flange 90. Avthreaded hole in the center of ange is adapted to receive an externally threaded plug 9|. 75

93 in plug 9 I. One end of the rod 94 abuts against the head of plug 95 (similar in all respects except shape to plug 35 of Fig. 1). On the other end of rod 94 is threaded a collar 96, adapted to hold a spring 91 in compression between itself and the plug 89. Further, the collar 96 is adapted to abut against the inner face of plug 9| in a manner and for a purpose to be hereinafter made clear. A

. key 98 on the rod 94 cooperates with the keyway formed in the plug 89. An annular collar 99, formed on the rod 94 engages the inner face of plug 89 under certain conditions which will be made clear hereinafter.

The application of the instrument of Fig. 5 to an air conditioning system is shown in Fig. 1l. The apparatus shown in Fig. 11 is identical with the apparatus of Fig. 10, except that a differential thermostat |00 (see Fig. 5) has been substituted for of Fig. 10. The operation of the dampers 53 and 54, and where desired, the control of spray temperature in 49, by thermostat 60 to control the dewpoint of air passing through air washer 49 is identical with the operation of the same elements in Figs. 9 and 10. Likewise, the valve 59 is open when there is no air pressure on its diaphragm and closes vas the pressure increases to 5 pounds per square inch. Dampers 51 are open a minimum amount when the air pressure in line 66 is 5 pounds per square inch or below, and are open a maximum amount when the pressure increases to 10 pounds per square inch. Further, dampers 56 are fully open from 0 pounds per square inch, start closing at 5 pounds per square inch, and are fully closed at 10 pounds per square inch.

In Fig. 11 the element I3 of thermostat |00 re- A-sponds to changes in temperature ofthe air in discharge duct 5|.

The other temperature responsive element 8 1, of thermostat |80, is influenced by outside air through sampling tube 86.

Assuming, for illustrative purposes, that rod 94 has been adjusted, hence, plunger 21 and seat |8, so that any movement of tube I3 tends to increase or decrease the airpressure in line 66,

thereby causing. the operation of valve 59 and dampers 56and 51 to maintain a constant temperature of '10 F. in duct 5 I and further, that the with Figs. 1 and 3, forces the plunger 21 and its related parts vto the right, thereby keeping the head of plug 95 constantly against the end of rod 94. A movement of plunger 21 and the valve seat I8 to the right obviously increases the opening between the seat i8 and the head I1, hence, increasing the pressure of air in the line 66. Any increase in pressure, as has been'repeatedly pointed out, causes a consequent decrease in temperature in duct 5I As the outside temperature continues to rise, the tube 81 will respond in the` above described manner until a temperature of 70 F. is reached. At this point (70), the collar 96 will engage the face of plug 9|. Any fur- 5 ther movement of rod 94, to which the collar 96 is threaded, will be' impossible. Therefore, any

- further movementl of the plungerv21 and seat I8 becomes impossible. It is apparent that the .movement f tube I3 and head |1 alone affects 1f() the air pressure in line 66 once the collar rests against 9|, hence, once this collar does engage 9|, the thermostat I3 will tend to hold a cnstant temperature in duct 5|. Any further expansion of the tube 81 will cause plug 89 to slide 15 along rod 94, to which it is keyed, and compress spring 91. Conversely, as the temperature affecting 81 drops, the tube contracts. At 70 F.,

' the plug 89 lengages the annular collar 99 of rod 94 and forces the rod tothe left. This move- 20 ment of rod 94 causes a simultaneous movement of the plunger 21 and seat I8, thereby closing the valve, decreasing the air pressure on line 66 and consequently increasing the temperature within duct 5|.' 25 The functions of the adjusting members of the instrument shown in Fig. 5 is most clearly understood by reference to Fig. 6, which shows the variations in temperature in duct 5| of Fig.'11 with respect to variations in outside temperature. "30 The sloping portion of the curve is secured when the instrument is functioning differentially, to

.Wit, when both the head I1 and the seat 8 are subject to movement by their respective expanding members I3 and 81. As was previously ex- 35- plained, the slope (degrees variation in duct temperature per degree variation in outside temperature) is determined by the ratio of the lengths of the expanding members, and for any given instrument, this slope is fixed. 40

' The horizontal portion of the curve represents a constant temperature which will be held regardless of outside temperature. This portion of the curve is obtained when only the headi |1 is subject to movement. 45

The intersection of the sloping .portion with the horizontal portion of the curve represents the point at which the stop member functions to prevent further movement'of the seat, that is, when collar 98 abuts' against the faceof plug 9| 50 In adjusting the instrument, the inner rod 94 is rotated, hence, plug 89, through key 98, is advanced, or retracted, thereby advancing or retractin'g the rod. Obviously, any movement of the rod moves plunger 21 and .the valve seat I8 55 `associated therewith. The valve seat is set, by this means, until air pressure in the line 66 is suicient to voperate valves 59 and dampers 56 and 51, to give a desired temperature (in this case' 70 F.). Thereafter, any change in tem- 60 perature in duct 5| will be reflected by a movement of tube I3 and head |1 to open or close valve 59 and thedampers to restore a temperature of 70 F. in duct 5|. It is understood that the temperature 70 F. is merely illustrative and 65 that the instrument could be set in the above manner to hold any desired temperature.

It is further'understood that the plug. 9| may be advanced or retracted so that it engages the collar 98 at any desired temperature, 70

With particular reference to Fig. rI, a flange |0 similar in all respects to flange 39 of Fig. 1,

'is threaded on the end of casting 25. The invar rods or the like, 49 are suitably fastened to flang |8| at one of their ends, the other Veli/dsv sup- 'Il porting a ilange |02. The iiange |02 is bored axially and internally threaded to receive a threaded plug .|03. The member |04 is screwed into plug |03 tightly enough to lock the two together. The plug |03 is drilled axially, as'shown, so as to provide a flange on its inner face. The outer end of |03 is internally threadedv to receive an externally threaded member |04. A hole in the member |04 is adapted to receive the threaded end portion of an invar rod or the like, |05.

The other end of the rod |05 has a head |06 formed thereon over which a cap |01 tits. The

cap 01 is threaded or otherwise fastened to the end of head lot which except for shape is identiported, .but the tube is not attached either Vto |01 or to |09. The tube IIZ is similar to tube 41 of Fig. 1 and is preferably of the same material, vfor example, brass.

The diierential thermostat shown and described in connection with Fig. 7, generally. designated II3, is shown in Fig. 12 applied to an air conditioning system. In this case, the thermostat I.|3 replaces thermostat 60 of Figs. 9, -10 and 11 and is adapted to control the dewpoint temperature of. air passing through washer 49 by controlling the operation of dampers`53 and 54 and the mixing valve II4. -As contemplated by applicant for this particular case, damper 53, controlling the admission of outside air, is normally open when air pressure on its operating motor 63 is 0 pounds per square inch, starts closing as the pressure increases to 2 pounds per square inch and is closed a maximum amount when the pressure reaches 5 pounds per square inch. Conversely, damper 54 is normally fully closed when the pressure on its operating motor 62 is 0 pounds per square inch starts to open as the pressure increases above 2 pounds per square inch, and is fully open when the pressure reaches 5 pounds per square inch.

The pump ||5 isadapted to draw water from the sump of air washer 49 either through the reirigerating machine I6, or through a bypass pipe ||1, or through both, and is adapted to deliver the water to spray devices within air washer 49. By varying the amount of water drawn throughJ the refrigerating machine and mixingwith it unrefrigerated water (through pipe ||1) the temperature of the mixture can be controlled. This is accomplished by means of. a three way (or mixing) valve, the construction of which is so well known as to require no lengthy explanation. Suillce it to' say that the mixing valve |I4 is so arranged in the water circuit that when air pressure on the diaphragm of the valve is below 5 pounds per square inch, pump I I5 draws its entire supply of water through pipe ||1. As the pressure increases above 5 pounds, the valve operates to allow the pump to draw a part of the water through. the refrigerating machine and part through pipe II1 and when the pressure reaches 10 pounds per square inch the entire volume of water will be drawn through the refrigerating The differential thermostat I I 3 is mounted on air washer 49 so that element I3 responds to changes in temperature of the air within the washer. The other thermal element I|2 is inuenced by changes in temperature of outside air 5 through sampling tube 96.

Specifically, the adjustment of ||3 is as follows. The seat |9 is adjusted, by rotating member |04 and plug |03, as a unit until the pressure in line 6|, connecting the discharge passage of |I3 to the mixing valve I4 and damper motors B2 and 63, is just sufficient to maintain the dewpoint temperature in washer 49 at any desired point. Rod I05-is then rotated until head |06, at 70 F. (or any other desired temperatl'lre) 15 firmly engages the shoulders of cap |01. In adjusting the instrument, tube IIZ, at the desired cut oi temperature (70 F. in this'case) should `be iirmly engaged between |01 and I 09, and the collar ||0 should be resting againstthe flange 29 of plug |03, so that any expansion of the tube will hold |01 against the head |09 and compress spring III. Further, any contraction of I|2 will allow the head |01, hence seat |I9, to move to the right under the influence of air pressure 25 in chamber 26.

Assuming that the instrument has been ad- )justed as above described so that the element I3 tends to hold a constant temperature of 60 F. in air washer 49, and the tube II2 holds cap |01 30 against I09 when the outside temperature is 70 F. or above, the operationof the instrument to control the `dewpoint according to the schedule of Fig. 8 is as follows. Y

It is apparent that as long as the outside tem- 35 perature isabove 70 F., the I I2 will hold |01 firmly against head |06, hence, only the thermostatic element I3 will function. Assuming that the outside temperature is above '10 F., any rise in temperature in the washer 49 will cause ele- 40 ment I3 to expand and open the air valve, thereby increasing the air pressure in line 6I. An' increase in pressure in 9| will tend to close the fresh air damper 53 and open return air damper 54. If this is not suiilcient to bring the tempera- 45 ture in washer 49 down to the desired level, the valve ||4 will act to allow the passage of water through the reirigerating machine. If, however, the temperature in the air washerwas below the desired level, element I3 would contract, thereby 50 reducing the pressure in line 6|. A reduction in pressure would iirst act on valve I4 to reduce the amount of refrigerated water. If the tem- .perature were still too low, damper 54 would start to close and 53 to open.

Assuming that the outside temperature is falling, it is apparent that tube |I2 will contract. 'I'he spring III will rst expand until collar I|0 rests against the ilange of plug |93. At 70 F.,

as was explained, the collar will be against the 50 flange and the tube will be holding |91 firmly against head |06. Any further contraction of tube II2 will allow the shoulders of |91 to move Aaway from |06 (under the action of air pressure lthermosta'tic elements operative responsive to temperature changes in two mediums, thus to provide diierential temperature control. How- 75 stop element islpr'ovd'edfor limiting the effectivel operation offonle of the thermostatic elements.

.l Asis apparentfrom'the'foregoing description, Whenever'the stop element prevents a movement of thevalve lseat, then only one of the thermostatic element-s is operative as a control means.

'I'hereafter,: the instrument operates as a straight v thermostat, i. Le., it 'responds to temperature changes in one medium only. Consequently, then, the stop elementgserves to change the entire character of the instrument, i.l e., from a diil'erential to a straight thermostat,`and vice versa.

Since certain changes in carrying out the above process and in the constructions set forth, which embody the invention may be made without departing from its scope, it is intended that all matter contained in the vabove description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. A control device of the-character described having a plurality of movable members adapted to regulate the iiow of fluid, one of said members being under the control of a movable element adapted to contract and expand through a certain distance within a certain range of temperatures, the other member being under the control of another movable element adapted to contract and expand through a different distance within the same range of temperatures and an adjustable stop element for terminating the movement ofsaid other member.

2. In a control device of the character described, a pressure regulating means,'said means comprising a valve seat and a closure member, means responsive to temperature changes in one medium for operating said closure member, means operative responsive to temperature changes in a second medium for operating said seat member,v

and means for stopping the movement of said seat member whenever the temperature of said second medium attains a desired point.

3. In a control' instrument, a valve, a iirst thermostatic member, a second thermostatic member, said members being adapted to operate said valve responsive to temperature changes in mediums affecting said members, and means for means being adapted to move equal distances responsive to unequal temperature changes and adjustable means for stopping the movement of the seat whenever the temperature of the first medium attains a desired point whereby the instrument provides differential thermostatic control prior to the stoppage of said seat and straight thermostatic control during the stoppage of said seat.

5. In a control device of the character described, a valve comprising a movable seat and a movable closure member, a iirst thermostatic element responding to temperature changes in a first medium for moving said seat, a second thermostatic element responding to temperature changes in a second medium for moving said closure member, means for stopping the movev5 ment of said seat whenever the temperature ofthe first medium rises above a desired point, said means being adjustable to vary the point at which the movement of said seat is stopped, and an escapement means whereby the rst thermo- 10 static element may continue to vmove'after the seat has been stopped.

v6. A control device of thecharacter described having a plurality of movable members adapted to regulate the iiow of liquid, one of said mem- 15 bers being movable under the control of a i'irst thermostatic element having a certain rate of expansion, the other member being movable under the control of a second thermostatic element having a different rate of expansion, said first 20 element being operative responsive to temperature changes in a iirst medium, said second element being operative responsive -to temperature changes in a second medium, and an adjustable stop element for limiting the movement of one 25 of said movable members when the temperature affecting its associated thermostatic element attains a. desired point.

7. In a control device of the character described, a valve comprising a movable seat and 30 a movable closure member, a thermostatic device operative responsive to temperature changes in a first medium for moving said seat; a thermostatic device operative responsive to temperature changes in a second medium for moving said 35 closure member, and means forv stopping the movement of said seat whenever the` temperature of said first medium attains a desired point, said means being adjustable to vary the point at which said seat is stopped.

8. In a control device of the character described, a valve comprising a movable seat and a movable closure member, thermostatic means operative responsive to temperature changes iny a first medium for moving said seat member, thermostatic means-operative responsive to temperature changes in a second medium for moving said closure member, and means for stopping the movement of said seat whenever the temperature of said iirst medium attains a desired point.

9. In a thermostatic control device, a valve comprising a movable closure member and a movable seat, thermostaticl means operative responsive to temperature. changes in one medium for moving said closure member, thermostatic means operative responsive to temperature changes in a second medium for moving said seat, and means for stopping the movement of said seat whenever the temperature of the iirst medium attains a desired point whereby the device provides diierential thermostatic control prior to the stoppage of said seat and straight thermostatic control during the stoppage of said seat.

l0. In a control valve, a valve seat, a closure member, means operative responsive to temperature changes in a iirst medium for moving said seat, means operative responsive to temperature changes in a second medium for moving said closure member, said means being adapted to move equal distances responsive to unequal temperature changes, and means forstopping thev movement of said seat Whenever the temperature of said rst medium attains a predetermined point, said last means being adjustable to vary the temperature at which said seat is stopped.

11. In a control device, a valve seat member, a closure member, a rst thermostatic element for moving the seail member, a. second thermostatic element for moving the closure member, and means for stopping the movement of one of said members at a predetermined temperature, said means being adjustable to vary the point at which the memberv is stopped; whereby the iustrument provides thermostatic control in response to temperature changes in two mediums prior to the stoppage of the member, and thermostatic control in response to temperature kchanges in one medium after the stoppage of the 

